MIMO (Multiple Input Multiple Output, multiple input multiple output antenna system) and Beam forming (beamforming) technologies are widely applied in current wireless high speed communication systems. Especially, a 3GPP LTE (Long Term Evolution, long term evolution) system requires all LTE UEs (User Equipment, user equipment) to support the MIMO technology, and meanwhile a TDD (Time Division Duplexing, time division duplexing) mode of the LTE requires the UE to support the Beam forming technology.
The MIMO is a multi-antenna technology in the wireless communication system, which mainly uses a plurality of antennas at a transmitting end to individually send signals independently, and meanwhile uses a plurality of antennas at a receiving end to receive information, thereby effectively enhancing spectrum efficiency of the wireless communication system, so as to greatly increase system capacity and possible transmission distance. With regard to the MIMO technology, obtaining a diversity gain or a multiplexing capacity by means of non-correlation is a critical way to enhance the system capacity. Therefore, as for the UE the correlation between antennas needs to be reduced as much as possible, so that mutual impact between spatially parallel sub-channels becomes smaller. In this way, in the transmit diversity technology, it is more convenient to obtain a diversity gain; and in the spatial multiplexing technology, it is more convenient to obtain a multiplexing capacity.
The Beam forming technology is another multi-antenna technology, the principle of which lies in using high correlation of spatial channels to implement beamforming, so as to enhance signal-to-noise ratio, and increase system capacity or coverage scope. With regard to the TDD mode of the LTE, an eNB (evolved NodeB) makes a downlink channel evaluation mainly by using channel interchangeability according to a pilot frequency sent by a user end, so as to implement the beamforming.
However, the current LTE UE generally supports using one antenna for transmission and two antennas for reception, that is, the so-called manner of one for transmission and two for reception; meanwhile, the optimal performance of the MIMO is required. Therefore, orthogonal polarization and the like are adopted to reduce the correlation between two receive antennas as much as possible, so as to obtain higher diversity gain and multiplexing capacity. However, the UE in the TDD mode of the LTE must support the Beam forming technology, the evolved NodeB in the TDD system utilizes the interchangeability between uplink and downlink channels to make the beamforming, and since the UE usually adopts a manner of uplink single transmit antenna, that is, the beamforming is made with respect to the single transmit antenna. Thereby, the gain brought by a low antenna correlation satisfying the MIMO optimal performance is lower than the gain brought by a high antenna correlation, and such a low antenna correlation may obviously affect the gain of the Beam forming, thereby affecting the cell coverage scope and system capacity.